It is known that polyurethane, a thermoplastic elastomer and the like excellent in hydrolysis resistance, light resistance, oxidative degradation resistance, heat resistance and the like are obtained when polycarbonate diols are used as a soft segment thereof. However, since a polycarbonate diol using 1,6-hexanediol as a raw material is highly crystalline, the polycarbonate diol cannot be used as a raw material for coating materials. In order to solve these problems, an aliphatic copolycarbonate diol using two or more types of diols is disclosed. Particularly among them, an aliphatic copolycarbonate diol using 1,5-pentanediol attracts attention as a polycarbonate diol which has a low crystallinity and can provide a polyurethane and a thermoplastic elastomer excellent in flexibility and elastic recovery (see PATENT DOCUMENT 1).
In the case where a polycarbonate diol is used as a raw material for polyurethanes, thermoplastic elastomers, urethane elastic fibers and the like, or as a constituent material for coating materials, adhesives and the like, the polycarbonate diol is reacted with a compound having a functional group reactive with a hydroxyl group, such as an isocyanate. Herein, stabilizing the reaction of the compound having a functional group reactive with a hydroxyl group with the polycarbonate diol is very important from the viewpoint of the production and the product quality. A polycarbonate diol is easily macromolecularized by the above-mentioned reaction, and in order to obtain a target molecular weight, a high technology to control the reaction is conventionally needed. There further arises such a problem that the polycarbonate diol is partially macromolecularized and produces fine gel, which imparts a problem to the product quality. On the other hand, in the case of a low reaction rate, since the macromolecularization hardly occurs and the molecular weight distribution broadens, there also arise problems of the tackiness of the surface due to low-molecular weight substances and of decreased physical properties such as strength and impact resilience.
In order to control the reaction rate in the above-mentioned reaction, various types of polycarbonate diols and manufacturing methods thereof have been disclosed hitherto. For example, there is disclosed a manufacturing method of a reactivity-stabilized polycarbonate diol using a carbonate containing a moisture content made to be 15 ppm or less as a raw material (see PATENT DOCUMENT 2). The method requires a dehydration process for the carbonate, and additionally cannot provide a sufficient effect on the reaction stabilization in some cases.
On the other hand, as methods paying attention to terminals of polycarbonate diols, there are disclosed, for example, methods for manufacturing a polycarbonate diol whose terminals are almost completely consisting of hydroxyl groups by using a dialkyl carbonate or a diaryl carbonate, and a polyhydroxyl compound as raw materials (see PATENT DOCUMENTS 3 and 4). These methods aim at solving a problem that, in the case where a polycarbonate diol is manufactured using a dialkyl carbonate or a diaryl carbonate as a carbonate raw material, alkyl groups or aryl groups originated from the carbonate remain at polymer terminals, and thereby manufacturing a polycarbonate diol whose polymer terminals are almost all hydroxyl groups. However, PATENT DOCUMENTS 3 and 4 do not describe the type of the hydroxyl group at the polymer terminal and the control thereof, nor to the control of the reaction of the polycarbonate diol with a compound having a functional group reactive with a hydroxyl group.
A polycarbonate diol having a high primary terminal OH ratio is further disclosed (see PATENT DOCUMENT 5). However, in the case of a high primary terminal OH ratio, there arises such a problem that the reaction rate often becomes too high and the polycarbonate diol is partially macromolecularized and produces fine gel. There is also disclosed a polycarbonate diol whose hydroxyl group ratio of the polymer terminal is made to be a specified value (see PATENT DOCUMENT 6). However, with the disclosed ratio of the polymer terminal hydroxyl group, a high-molecular weight polyurethane cannot be manufactured in some cases; and only the ratio of the polymer terminal hydroxyl group is specified and there is no description regarding primary hydroxyl groups in the hydroxyl groups in PATENT DOCUMENTS 5 and 6.
As described above, technologies to date cannot present a polycarbonate diol which can provide a coating film exhibiting no feeling of roughness originated from fine gelatinous substances and no feeling of tackiness originated from low-molecular weight substances, and further having well balanced performances including hydrolysis resistance and heat resistance. The technologies also cannot present a polycarbonate diol which easily stabilizes the reaction and can provide a polyurethane and a thermoplastic elastomer having well balanced performances including hydrolysis resistance and heat resistance; excellent physical properties, such as strength and impact resilience; and high flexibility.    PATENT DOCUMENT 1: Japanese Patent No. 1822688    PATENT DOCUMENT 2: JP 2006-176704 A    PATENT DOCUMENT 3: U.S. Pat. No. 7,112,693    PATENT DOCUMENT 4: Japanese Patent No. 3724561    PATENT DOCUMENT 5: Japanese Patent No. 3874664    PATENT DOCUMENT 6: JP 2006-104253 A